Multivibrator is an electronic circuit that oscillates between the two states i.e high to low and vice versa, for producing a continuous output.
A pulse generator circuit like multivibrator produces clock pulses which are square and rectangular waveform and are continuous in nature.
They are basically of three types, depending on their state:
A brief characteristic of the various types are as follows:
They are also called Free running multivibrator/oscillator.
- They have no stable state
- Switches continuously between 2 states.
- They produces a train of SW pulses at fixed frequency.
- Their 50 % output is high and 50% output is low.
- The timing cycle is determined by RC time constant of the resistor capacitor- RC Network.
- They uses 2 CMOS NAND gates connected as inverting Not gate.
- T=2.2 RC
Application: Ideal for timing and clock pulse applications.
They are also called One shot multivibrator.
- It has only one stable state.
- They have pulses of specific duration.
- It is triggered externally.
- Generate a single o/p pulse either high or low with external trigger.
- They are made from two cross coupled NAND gate.
- T=0.69 RC
Application: Used to convert short sharp pulses into wider ones for timing applications.
This is also known as a “Bistable Latch“, “Toggle Latch” or simply “T-latch“.
- It is a SR Flip flop with addition of an inverter or NOT gate to provide the necessary switching function.
- They have two stable state either positive or negative.
- Their circuit will remain in either state indefinitely.
- They produces single pulse either positive or negative.
- It passes from one state to the other “only” when a suitable external trigger pulse T is applied.Two triggering pulses are needed, to go through a full “SET-RESET” cycle.
Application: Latches, counters, frequency dividers, storage devices in computer memory.